Technical data

Diagnostics
23.9 Program Measures for Handling Errors
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 511
23.9.5 CPU Redundancy Error (OB72)
Description
The operating system of the H CPU calls OB72 if one of the following events occurs:
• Loss of redundancy on the CPUs
• Comparison error (for example, RAM, PIQ)
• Standby-master switchover
• Synchronization error
• Error in a SYNC submodule
• Update process aborted
• OB72 is executed by all CPUs which are in RUN mode or STARTUP mode after an
accompanying start event.
Programming OB72
You must create OB72 as an object in your S7 program using STEP 7. Write the program to be
executed in OB72 in the generated block and download it to the CPU as part of your user program.
You can use OB72, for example, for the following purposes:
• To evaluate the start information of OB72 and determine which event triggered the loss of CPU
redundancy.
• To determine the status of your system using SFC51 RDSYSST (SZLID=B#16#71).
• To react to the loss of CPU redundancy specifically for the plant.
The CPU does not change to STOP mode if a CPU redundancy error occurs and OB72 is not
programmed.
You can find detailed information on OBs, SFBs, and SFCs in the corresponding Help on Blocks.